linux-kernel - Re: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

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Date: Wed, 3 Jan 2024 08:48:46 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Yi Liu <yi.l.liu@...el.com>, "Tian, Kevin" <kevin.tian@...el.com>,
	"joro@...tes.org" <joro@...tes.org>, "alex.williamson@...hat.com"
	<alex.williamson@...hat.com>, "robin.murphy@....com" <robin.murphy@....com>,
	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>, "cohuck@...hat.com"
	<cohuck@...hat.com>, "eric.auger@...hat.com" <eric.auger@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "mjrosato@...ux.ibm.com"
	<mjrosato@...ux.ibm.com>, "chao.p.peng@...ux.intel.com"
	<chao.p.peng@...ux.intel.com>, "yi.y.sun@...ux.intel.com"
	<yi.y.sun@...ux.intel.com>, "peterx@...hat.com" <peterx@...hat.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"shameerali.kolothum.thodi@...wei.com"
	<shameerali.kolothum.thodi@...wei.com>, "lulu@...hat.com" <lulu@...hat.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>, "Duan,
 Zhenzhong" <zhenzhong.duan@...el.com>, "joao.m.martins@...cle.com"
	<joao.m.martins@...cle.com>, "Zeng, Xin" <xin.zeng@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
Subject: Re: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d
 stage-1 cache invalidation

On Wed, Jan 03, 2024 at 12:01:08PM -0400, Jason Gunthorpe wrote:
> On Wed, Jan 03, 2024 at 10:24:42AM +0800, Yi Liu wrote:
> > On 2024/1/3 07:38, Jason Gunthorpe wrote:
> > > On Fri, Dec 15, 2023 at 12:01:19PM +0800, Yi Liu wrote:
> > > > > I think I misread Yi's narrative: dev_id is a working approach
> > > > > for VMM to convert to a vRID, while he is asking for a better
> > > > > alternative :)
> > > > 
> > > > In concept, dev_id works, but in reality we have problem to get a dev_id
> > > > for a given device in intel iommu driver, hence I'm asking for help here. :)
> > > 
> > > I think we just need to solve this one way or another.. Even if you
> > > use a viommu object you still end up having difficult coupling to
> > > iommufd
> > > 
> > > Some:
> > >    iommufd_get_dev_id(struct iommufd_ctx *ictx, struct device *dev)
> > > 
> > > Callable by a driver (using the driver-callable function
> > > infrastructure we made for dirty tracking) Is really all that is
> > > needed here.
> > 
> > yep, I noticed IOMMUFD_DRIVER was selected by intel iommu driver when
> > IOMMUFD is configed. Maybe such an API could be compiled when
> > IOMMUFD_DRIVER is enabled as well. This does address my concern on making
> > intel iommu driver depending on iommufd. But still need a way to pass in
> > the iommufd_ctx pointer to intel iommu driver, and store it. Hence intel
> > iommu driver could call the above iommufd_get_dev_id(). One possible way is
> > passing it when attaching device to domain and clear it in detach. However,
> > this seems not ideal as iommufd_ctx information should be static between
> > bind_iommufd and unbind. But we don't call into intel iommu driver in the
> > bind and unbind operations. May need to add new iommu op. Any suggestion
> > here?
> 
> You can pass the ctx to the invalidate op, it is already implied
> because the passed iommu_domain is linked to a single iommufd ctx.

The device virtual id lookup API needs something similar, yet it
likely needs a viommu pointer (or its id) instead? As the table
is attached to a viommu while an ictx can have multiple viommus,
right?

Thanks
Nic